PROTEIN FROM OIL : THE BP ALKANE PROCESS

PROTEIN FROM OIL : THE BP ALKANE PROCESS K. ALLISON BP PROTEINS LIMITED, GRANGEMOUTH, STIRLINGSHIRE, SCOTLAND 1. INTRODUCTION The fact that yeasts will grow on hydrocarbons has been known from the early partı ofthis century when some of the first academic papers were published. The use of yeasts as animalfeed is well established and now large amounts of fodder yeast grown on carbohydrate are produced in the world based on wood pulp liquor. The novel development described in this paper is the continuous growth of yeasts on pure hydrocarbons on a commercial scale. Work in this field by BP started in ca 1957 with the studies by A. Champagnat of Societe Francaise des Petroles BP (SFBP) into the microbial oxidation of petroleum fractions. Initially the objective was desulphurisation, but in the course of this work he discovered, surprisingly, that the n-paraffins in the petroleum fraction wereutilised selectively by the micro-organism. This and the realisation that there existed in this field the basis of a commercial process for the production of protein concentrate led, in 1959, to the re-orientation of the work at Lavera to the complementary objectives of protein production and oil de-waxing. Progress was rapid. 74 K. Allison By 1962 Champagnat and his co-workers had published papers on the production of protein concentrate from oil fractions and it was in 1963 that the development phase got underway with the commissioning at Lavera, near Marseilles of a ca k te/d pilot plant producing yeast on a continuous basis from a refinery gas oil stream. A year later, a study on the growth of yeasts using pure n-paratfins as the carbon substrate was commenced by BP at Grangemouth, Scotland. Although the initial aim of this work was to support the gas oil process under development at Lavera and to obtain a more fundamental knowledge of hydrocarbon fermentation, this period in the mid 1960's coincided with the introduction of large scale commereralplants 'for'the 'extraction of'highly’püre n-paraffins using molecular sieve technology and, it soon became apparent that here wasthe basis of a second process forthe production of protein concentrate. Of the two processes developed by BP for the production of protein concentrate the "Gas Oil' Process and the ‘Normal Paraffin' Process,the present paper is principally concerned with the latter routesince this is the process with which the author has most first hand knowledge and it is the basis of the 4000 t/a Demonstration Unit at Grangemouth. ts Re BP Alkane Process 19 The product of the BP 'Normal Paraffin' Process is marketed in various forms under the registered trade mark TOPRINA. 2.0 THEY BP na>=PARAPRINS (PROTEIN: PROCESS 221 °Process The production of yeast can conveniently be divided into: ( i) feed materials ( ii) fermentation and(iii) harvesting A simplified flow diagram is shown in Figure l. EPICURE IL. BP n-Paraffin Protein Process. RAW FERMENTATIO MATERIALS N HARVESTING AND DESPATCH VENT VENT SEPARATED HOT WATER AIR INOCULUM MINERALS ——o— et WATER. D DPARAFFINS m AIR u | FINISHED BP PROTEIN S SEPARATOR F FERMENTER CONCENTRATE. St STERILIZER € COOLER OR CONDENSER Bb DRYER V STORAGE VESSEL 76 K. Allison The fermentation step is the core of the process and an essential feature of the n-paraffins based route is that the fermentation is operated under applied aseptic conditions. This means that all yeasts other than the specifically developed culture yeast strain are excluded from the fermenter, and to ensure the sterility of the fermenter at start-up, it is sterilised by steam prior to being charged. It is important to note that no pathogenic bacteria have ever occurred in our hydrocarbon fermenters. (i) Feed Materials: The liquid feeds to the fermenter comprise n-paraffin, water, nutrient mineral salts and essential growth factors, The paraffin feedstock, the carbon source, isa highly pure material of Pharmacopoeia standard and passes FDA test 121/1146. It is a colourless, odourless material of high normal paraffin content, 99%, on which strict limits are imposed on the aromatics content. The quality of the feedstock is an important factor in the quality control of the final product Since, unlike the 'Gas Oil' Process, the protein product from the n-paraffin process is not subjected to a final solvent extraction stage. BP Alkane Process a7 The mineral salts which are those essential forthe optimum growth of the organism include e.g. sulphates of Zn, Mn, Mg etc. and they are prepared as a concentrated acidified solution which is then continuously diluted with water to the required medium concentration. Tight specifications .are set on the quality of these salts as an essential part of the quality control of the final product. To ensure the applied aseptic nature ofthe fermentation, these liquid streams are combined and passed to the medium sterilisation system where they are heated and held at a high temperature sufficiently long to ensure complete "kill" of all micro-organisns. Heat economy is achieved by exchange between the incoming cold feed and the hot sterilised feed. The cooled sterilised medium passes directly to the fermenter. Oxygen necessary for cell growth is provided by a continuous stream of air blown into the fermenter through a sparge ring andthe excess airand carbon dioxide pass to atmosphere. 78 K. Allison Nitrogen, essential for the growth of the organisn, is injected in the form of ammonia with theair stream. The ammonia serves also to maintain the fermenter contents at the required pH, the addition rate being automatically controlled by the pH in the fermenter. The combined air and ammonia stream is sterilised. (ii) Fermentation At the start of the operation, a small batch fermentation is set up to provide an inoculum for the production fermenter, and its completion synchronised with the charging of a sterilised batch of medium (water, n-paraffin, salts etc.) which has been pH adjusted by the addition of ammonia. The inoculum is injected into the production fermenter, sterilised air admitted and agitation commenced. The batch growth in the production fermenter is allowed to proceed until the dry cell weight reaches the required level after which the process is run as a truely continuous operation with the fermenter under steady state conditions. Fresh sterilised liquid feeds are passed into the fermenter and the broth (the aqueous phase containing the yeast, excess salts and a very small amount of excess paraffin) is, etaken off into the harvesting section under liquid level control. BP Alkane Process 19 The heat evolved in the fermentation togetherwith the optimum growth temperature of ca 90°C, necessitates cooling which is provided by circulating the fermenter contents through an external heat exchanger. The intimate mixing of the four phase system to effect the efficient transfer of hydrocarbon, essential minerals and oxygen to the cells is achieved by a combination of air sparging and mechanical agitation. The fermenter variables, notably dilution rate, temperature, pH, agitation andair supply rates are optimised so as to leave as little hydrocarbon unconsumed as possible. (iii) Harvesting Harvesting is essentially a two stage water removal operation comprising centrifugation and spray drying. The continuous product stream (broth) from the fermenter is processed in a yeast/water continuous centrifugal separator which separates a clear aqueous phase and a yeast cream containing about 15% solids. The aqueous phase can then either by recycled or passed to an effluent plant for treatment. 80 K. Allison The yeast cream is then passed to the final spray drying stage. The spray dried powder containing 5-6% weight moisture is discharged from the drier chamber and cyclone separators into a pneumatic conveying system and transported to storage hoppers from which it can be bagged-off or loaded directly in bulk for despatch. Although centrifugation and spray drying are well established techniques, their use in the present process presented new problems and considerable knowhow has had to be developed to ensure a high on-stream efficiency for the equipment and reproducible microbiological quality of the product. in (fact the plant is virtually built to human food standards. Stainless steel is used throughout most of the plant, detailed attention has to be paid to engineering practice throughout the plant and rigorous cleaning procedures are adopted. 2.2 Product and Product Clearance The basic product is a buff free flowing powder which can be made available in different forms depending on the market outlet. To obtain product of the desired particle size, standard processes for agglomeration or attrition can be applied dependent on the market requirement. BP Alkane Process 81 Prior to despatch, the material has to be cleared both chemically and microbiologically. The chemical analyses cover, e.g. crude protein content, ash, phosphorus and residual hydrocarbon. Checks are also made on trace elements such as arsenic, antimony, lead, etc. though control of these at the required levels is exercised by quality control of the process input streans. The typical analysis of n-paraffins - grown yeasts is shown in Table 1. TABLE 1 | | Characteristics of Alkane-Grown Yeasts | Yeast: ¢ ı Moisture % wt <7 30 | Crude Protein (N x 6.25) % wt on 60 dry matter Lipids after acid hydrolysis % wt 8.-,.10 Ash % wt 6.0 Ca % wt 0.01 P S wt 1.6 Pepsin digestibility % 7 80 The crude protein content compares with fish meal and is considerably higher than that of soya at 45%. Because of the nature of the process, variations in product composition are very small so that the product quality is very consistent.